Security has become increasingly important in communication systems. In communication systems with inadequate security, messages can potentially be intercepted, read by unintended recipients, tampered with, and then forwarded on to original recipient as if the message was sent directly from the original sender. Accordingly, message security must be robust to ensure that parties are who they claim to be, to protect the confidentiality of sensitive information, and to prevent tampering with the data. In one approach to providing security, electronic messages may be encrypted by a sender and decrypted by a recipient using a public/private key mechanism. Another approach is for a sender to digitally sign messages.
One protocol for providing for digital signatures and encryption in massaging systems is S/MIME (Secure Multipurpose Internet Mail Extensions). S/MIME allows a sender to digitally sign messages using a private key, encrypt messages with a recipient's public key, or both digitally sign and encrypt the message. When a signed message arrives at a recipient's message server that supports S/MIME, its message signature is verified. A failing signature indicates that the message may have been tampered with. Thus, if the message signature does not verify correctly, the message is invalid. A message will also be invalid if it is signed with a key having a matching certificate that is weak, revoked, untrusted or expired. Similarly, a message encrypted with a recipient's public key (typically made available to the sender in a security certificate associated with the recipient) is able to be decrypted by the recipient who uses the matching private key.
Typically, in existing electronic communications systems, when an S/MIME message is determined to be invalid it is delivered to the intended recipient with an accompanying notification that the message is invalid. The intended recipient is put on notice that the message is not a valid, secure message. However, delivering such an invalid message to the recipient is often not a prudent course of action. Many massaging system users routinely disregard such warnings and open the message. In security conscious organizations, it is beneficial that message recipients do not have the opportunity to ignore such security warnings. It is therefore desirable to have a system and method for handling invalid messages prior to the recipient having a chance to view the message.